This invention relates to an oscillator, and more particularly, but not exclusively, to a multiple frequency oscillator.
There are many applications for an oscillator that operates at a precisely controlled frequency. Radio devices, such as radio sets and radio controlled toys employ an oscillator to generate a signal for demodulating an RF signal received by the radio device. In such radio devices, the oscillation frequency is set by a crystal and it is necessary to remove the crystal in order to change the oscillation frequency.
Digital frequency synthesis, in which a model signal is sampled at a first clock frequency and reconstructed using a second clock frequency, is used in spectrum oscillators for generating a replica of the model signal at any one of several precisely controlled frequencies, but is a rather expensive solution to the problem of providing multiple frequencies when it is only necessary to provide a choice among a small number of different frequencies.
Other circuits used for operating at a selected one of multiple frequencies are difficult to manufacture because they are very sensitive to component variations.